In a machining center of the center-through (spindle-through) coolant type shown in FIG. 9, a machining center 200 includes a processing table 205, a main shaft 210, a tool 220, and a coolant nozzle 240. To the processing table 205, a work 400 which is an object to be worked on is fixed. A coolant pump 100 shown in FIG. 9 is the type of pump that discharges a low-pressure coolant and a high-pressure coolant from one pump.
A high-pressure line Lh of the coolant pump 100 communicates with the tool 220, and a low-pressure line Ll of the coolant pump 100 communicates with the coolant nozzle 240.
The coolant pump 100 is attached to a coolant storage tank 300.
In the machining center 200 shown in FIG. 9, the low-pressure coolant discharged from the coolant pump 100 is supplied to the nozzle 240 and is jetted out of the nozzle 240 to the whole of the work 400. The coolant jetted out of the nozzle 240 to the whole of the work 400 removes chips during processing.
On the other hand, the high-pressure and clean coolant discharged from the coolant pump 100 is jetted from the tip of the tool 220. By jetting the coolant from the tip of the tool 220 at high pressure, cutting pieces are prevented from getting into the work 400, for example, whereby processing accuracy is improved.
The tool 220 for a high-pressure coolant shown in FIG. 9 sprays a coolant on the work to be worked on by making the high-pressure coolant flow through a coolant flow path passing through the center of the tool, and is a machine tool of the so-called “center-through coolant type.
In such a center-through coolant machine tool as shown in FIG. 9, it is important to control the spraying of the coolant appropriately to perform machining accurately.
A technique of performing control by which so-called constant-horsepower operation is performed in such a way that the product of the pressure and the flow rate of a coolant becomes nearly constant can be proposed (refer to, for example Patent Literature 1).
However, in the control by which so-called constant-horsepower operation that makes the product of the pressure and the flow rate of a coolant nearly constant is performed, since there are two types of parameters to be controlled: a pressure and a flow rate, the control itself becomes complicated, which complicates a control system.